Clojure workshop

Clojure workshop
Alf Kristian Støyle
Andreas Jacobsen

Agenda
• Introduksjon - hvorfor er Clojure viktig

• Basic syntax

• Oppgaver

• Gjennomgang av oppgaver

• JSON over HTTP

• Oppgaver

• Gjennomgang

• Oppsummering

public class Account {
private long balance;
public final int accountNo;

public Account(long balance, int accountNo){
this.balance = balance; this.accountNo = accountNo;
}

public void debit(long debitAmount) {
this.balance -= debitAmount;
}

public void credit(long creditAmount) {
this.balance += creditAmount;
}

public long getBalance() {
return this.balance;
}
}


}

public synchronized void debit(long debitAmount) {
}

public synchronized void credit(long creditAmount) {
}

public long getBalance() {
}
}


}

}

}

public synchronized long getBalance() {
}
}

private volatile long balance;

}

}

}

}
}

public void transfer(Account fromAccount, Account toAccount,
long amount) throws Exception {

if (fromAccount.getBalance() < amount) {
throw new Exception("Not enough money!");
}
fromAccount.debit(amount);
toAccount.credit(amount);
}


synchronized (fromAccount) {
synchronized (toAccount) {


}



}
}
}


Object mutex1 = toAccount;
Object mutex2 = fromAccount;
if (fromAccount.accountNo < toAccount.accountNo) {
mutex1 = fromAccount;
mutex2 = toAccount;
}
synchronized (mutex1) {
}
}
}
}


Object mutex1 = toAccount;
Object mutex2 = fromAccount;
if (fromAccount.accountNo < toAccount.accountNo) {
mutex1 = fromAccount;
mutex2 = toAccount;

?
}
}
}
}
}
private volatile long balance;

}

}

}

}
}

(defn transfer [from-account to-account amount]
(dosync
(if (> amount @from-account)
(throw (new Exception "Not enough money!")))
(alter from-account - amount)
(alter to-account + amount)))

(dosync

(def account-a (ref 1000))
(def account-b (ref 800))

(dosync

(def account-a (ref 1000))
(def account-b (ref 800))

(transfer account-a account-b 300)

@account-a
; => 700

http://www.dehne.carleton.ca/research/multi-core

Concurrency
dreier som om å gjøre ﬂere oppgaver
omtrent samtidig

Parallelism
dreier seg om å dele en oppgave i mange
deloppgaver som kan gjøres concurrent

Clojure
• General purpose
• Lisp (List Processing)
• Funksjonelt
• Kompilert
• Dynamisk typet
• Tett knyttet til JVM’en

1
; => 1

"Hello World"
; => "Hello World"

1
; => 1

"Hello World"
; => "Hello World"

(class 1)
; => java.lang.Integer

(class "Hello world")
; => java.lang.String

(println "Hello " "world")
; “Hello world”
; => nil

Funksjonsnavn

; “Hello world”
; => nil

Funksjonsnavn Parametere

; “Hello world”
; => nil


,
; “Hello world”
; => nil

Preﬁks notasjon

,
; “Hello world”
; => nil

Methods.callStatic();
methods.callInstance();

callStatic();
callInstance();

this.callInstance();
methods.callStatic();

Methods.this.callInstance();
Methods.this.callStatic();

(println "Hello world")
; Hello world
; => nil

; Hello world
; => nil

(sum 1 2 3)
; => 6

; Hello world
; => nil

(sum 1 2 3)
; => 6

(+ 1 2)
; => 3

; Hello world
; => nil

(sum 1 2 3)
; => 6

(+ 1 2)
; => 3

(+ 1 2 3)
; => 6

; Hello world
; => nil

(sum 1 2 3)
; => 6

(+ 1 2)
; => 3

(+ 1 2 3)
; => 6

(+)
; => 0

1 + 2 * 3

1 + (2 * 3)

(+ 1 (* 2 3))

Funksjoner

(fn [& nums]
(apply + nums))

Funksjoner
(def sum
(fn [& nums]
(apply + nums)))

Funksjoner
(def sum

)

Funksjoner
(def sum
(fn [& nums]
(apply + nums)))

(defn sum
[& nums] (apply + nums))

Lister!
'(3 2 1)
; => (3 2 1)

(+ 3 2 1)
; => 6

Lister!
'(3 2 1)
; => (3 2 1)

(+ 3 2 1)
; => 6

(defn iterate
[f x] (cons x (lazy-seq (iterate f (f x)))))

Immutable collections
; List
'(3 2 1)

; Vector
[1 2 3]

; Set
#{1 2 3}

; Map
{1 "one", 2 "two"‚ 3 "three"}

Persistent data
structures
(def my-list '(3 2 1))
; => (3 2 1)

Persistent data
structures
(def my-list '(3 2 1))
; => (3 2 1)

(def my-other-list (cons 4 my-list))
; => (4 3 2 1)

Immutable records
(defrecord Person [fname lname])
; => user.Person

(Person. "Alf" "Støyle")
; => #:user.Person{:fname "Alf", :lname "Støyle"}

Immutable objects are always thread-safe.

Ren funksjonell
programmering

f(x) = x + 1

Clojures ﬁlosoﬁ
Verdier
Immutable/uforanderlig, primitiv eller sammensatt

Clojures ﬁlosoﬁ
Verdier
Identitet
En observert entitet som vi assosierer med en serie
relaterte tilstander (verdier) over tid

Clojures ﬁlosoﬁ
Verdier
Identitet
Tilstand
Verdien til en identitet i på et gitt tidspunkt

Clojures ﬁlosoﬁ
Verdier
Identitet
Tilstand
Verdien til en identitet i på et gitt tidspunkt
Tid
Relativ før/etter endring av identitet

Fra Rich Hickeys
“Are we there yet”

Reference types
• Atoms - synkron og ukoordinert oppdatering
• Agents - asynkron og ukoordinert oppdatering
• Refs - synkron og koordinert oppdatering

Reference types
• Atoms - synkron og ukoordinert oppdatering
• Agents - asynkron og ukoordinert oppdatering
• Refs - synkron og koordinert oppdatering
• Synkron perception

Atoms
(def an-atom (atom 0))
; => #'user/an-atom

Atoms
; => #'user/an-atom

(swap! an-atom inc)
; => 1

Atoms
; => #'user/an-atom

(swap! an-atom inc)
; => 1

(deref an-atom)
; => 1

Atoms
; => #'user/an-atom

(swap! an-atom inc)
; => 1

(deref an-atom)
; => 1

@an-atom
; => 1

Agents
(def an-agent (agent 0))
; => #'user/an-atom

Agents
; => #'user/an-atom

(send an-agent inc)
; => #<Agent@9b7c63f: 0>

Agents
; => #'user/an-atom

(send an-agent inc)
; => #<Agent@9b7c63f: 0>

@an-agent
; => ; 0 eller 1 ??

Agents
; => #'user/an-atom

(send an-agent inc)
; => #<Agent@9b7c63f: 0>

@an-agent (await an-agent)
; => ; 0 eller 1 ?? ; => nil

@an-agent
; => 1

Refs
(def ref-1 (ref 0))
; => #'user/ref-1

(def ref-2 (ref 0))
; => #'user/ref-2

Refs
(def ref-1 (ref 0))
; => #'user/ref-1

(def ref-2 (ref 0))
; => #'user/ref-2

(alter ref-1 inc)

Refs
(def ref-1 (ref 0))
; => #'user/ref-1

(def ref-2 (ref 0))
; => #'user/ref-2

(alter ref-1 inc)
; java.lang.IllegalStateException:
; No transaction running

Refs
(def ref-1 (ref 0))
; => #'user/ref-1

(def ref-2 (ref 0))
; => #'user/ref-2

(alter ref-1 inc)
; java.lang.IllegalStateException:
; No transaction running

(dosync (alter ref-1 inc))
; => 1

Refs
(dosync
(alter ref-1 inc)
(alter ref-2 dec))
; => -1

Refs
(dosync
(alter ref-1 inc)
(alter ref-2 dec))
; => -1

@ref-1
; => 2

@ref-2
; => -1

Refs
(dosync
(alter ref-1 inc)
(dosync
(alter ref-2 dec)))
; => -2

@ref-1
; => 3

@ref-2
; => -2

Software transactional
memory

memory
Transactional memory is to
shared-memory concurrency
as
garbage collection is to
memory management

memory
Atomic
Consistent
Isolated
Durable

Oppsummering
• Skiller tilstand og identitet
• Ingen mutable tilstand
• Ingenting blokkerer
• Clojure hjelper langt på vei med concurrency

Oppsummering
• Skiller tilstand og identitet
• Ingen mutable tilstand
• Ingenting blokkerer
• Clojure hjelper langt på vei med concurrency
• Mindre “accidental complexity”

Clojure syntaks
(Masse paranteser)

• REPL
• Syntaks
• Data strukturer
• Funksjoner
• Hvordan fylle ut oppgavene
• Hvordan ﬁnne hjelp

Akkurat samme, skrevet litt lenger

Noen som klarer å gjette hva dette blir?

En funksjon er også bare data

Dette er en funksjon (uten navn)

let lar deg binde lokale variable

Oppgaver!

Disse ligger under
clojure-workshop/test/
clojure-workshop/test/
(Dere ser ikke dobbelt)

c-w/$ lein test
c-w/$ lein test clojure-workshop.test.core

To streker: __ => En funksjon
Tre streker: ___ => En verdi

Alle testene er kommentert ut, ﬂytt
(comment
nedover for å kommentere inn tester

• http://clojuredocs.org
• http://clojure.org/cheatsheet
• Repl har innebygget hjelp
• (doc first)
• (find-doc “Returns the first item”)

• (apropos ‘first)
• (source first)

JSON
• JavaScript Object Notation
• http://www.json.org/
• It is easy for humans to read and write.
• It is easy for machines to parse and generate

{
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address":
{
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": "10021"
},
"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
{
"type": "fax",
"number": "646 555-4567"
}
]
}
http://en.wikipedia.org/wiki/JSON

{
"age": 25,
"address":
{
"city": "New York",
"state": "NY",
map },

"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
{
"type": "fax",
"number": "646 555-4567"
}
]
}

{
"age": 25,
"address":
{
"city": "New York",
"state": "NY",
map },

"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
vector {
"type": "fax",
"number": "646 555-4567"
}
]
}

(clojure.data.json/read-json "...")

{
:firstName John,
:lastName Smith,
:age 25,
:address
{
:streetAddress 21 2nd Street,
:city New York,
:state NY,
:postalCode 10021
},
:phoneNumber
[
{
:type home,
:number 212 555-1234
}
{
:type fax,
:number 646 555-4567
}
]
}

{
"age": 25,
"address":
{
"city": "New York",
"state": "NY",
},
"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
{
"type": "fax",
"number": "646 555-4567"
}
]
}

(get {:one 1 :two 2 :three 3} :one)
;=> 1

;=> 1

(:one {:one 1 :two 2 :three 3})
;=> 1

;=> 1

(:one {:one 1 :two 2 :three 3})
;=> 1

({:one 1 :two 2 :three 3} :one)
;=> 1

clj-http

(client/get "http://google.com")
=> {:status 200
:headers {"date" "Sun, 01 Aug 2010 07:03:49 GMT"
"cache-control" "private, max-age=0"
"content-type" "text/html; charset=ISO-8859-1"
...}
:body "<!doctype html>..."}

https://github.com/dakrone/clj-http

Oppgave
• Eksempel på twitter json i “twitter-java-search-json.txt”

• Skrive ut “tweet-text” fra live twitter søk

• Skriv ut encodings benyttet i resultat av live twitter søk

• twitter-java-search-json.txt

• Finn antall unike encodings

• Skriv ut tweets fra “world_ﬁnance”

• Skriv ut tweets som er replies

• API’er

• https://github.com/dakrone/clj-http

• http://clojure.github.com/clojure-contrib/json-api.html

Lyst til å lære mer?
• clojure.org

• 4clojure.com

• github.com/functional-koans/clojure-koans

Takk for oss :)
• Spørsmål:

• aks@knowit.no

• aja@knowit.no

• Oppgaver: github.com/andreaja/clojure-workshop

• Løsninger: github.com/andreaja/clojure-workshop/tree/solutions

Clojure workshop

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